Enriched acid gas for sulfur recovery

ABSTRACT

A system of enriching acid gas for feeding a sulfur recovery unit includes a contactor configured to separate an acid gas stream into a carbon dioxide rich stream and a purified acid gas stream, where the acid gas stream includes hydrogen sulfide, carbon dioxide, and hydrocarbons; a regenerator in fluid communication with the contactor such that the regenerator is configured to separate the purified acid gas stream to create a hydrogen sulfide rich stream and a hydrogen sulfide lean stream; and a recycle stream conduit fluidly coupled between the regenerator to the contactor and configured to supply at least a portion of the hydrogen sulfide rich stream from the regenerator to the contactor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of, and claims priority to, U.S. patentapplication Ser. No. 15/681,093, filed on Aug. 18, 2017, and entitled“ENRICHED ACID GAS FOR SULFUR RECOVERY,” the entire contents of whichare incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to systems and methods relating to enriching anacid gas for a sulfur recovery process.

BACKGROUND

Sour natural gas compositions can vary widely in concentrations ofhydrogen sulfide (H₂S), carbon dioxide (CO₂), and hydrocarboncomponents. The removal of H₂S from sour natural gas is referred to as asweetening process. Excess H₂S can be separated from the sour naturalgas and sent to a sulfur recovery unit (SRU) when the H₂S contentexceeds a sales gas specification limit. However, if the H₂S contentdoes not exceed the sales gas specification limit, alternative means fordisposing the H₂S can be limited and costly. For example, worldwideregulations generally limit the flaring of H₂S as a form of H₂Sdisposal.

SUMMARY

This specification describes technologies and methods relating to anacid gas enrichment process for increasing a concentration level ofhydrogen sulfide (H₂S) in an enriched acid gas.

In a first aspect, a method of sulfur enriching an acid gas stream in anacid gas enrichment system includes: (i) feeding an acid gas stream to acontactor, the acid gas stream comprising hydrogen sulfide (H₂S), carbondioxide (CO₂), and hydrocarbons; (ii) separating the acid gas stream inthe contactor to create a carbon dioxide rich stream and a purified acidgas stream; (iii) feeding the purified acid gas stream to a regeneratorfluidly connected to the contactor; (iv) separating the purified acidgas stream in the regenerator to create a hydrogen sulfide rich streamand a hydrogen sulfide lean stream, the hydrogen sulfide rich streamhaving a concentration of hydrogen sulfide; and (v) periodically feedingat least a portion of the hydrogen sulfide rich stream exiting theregenerator to the acid gas stream entering the contactor.

In some embodiments, the periodically feeding step comprises adjusting arecycle valve disposed along a fluid pathway that directs the hydrogensulfide rich stream exiting the regenerator to the acid gas streamentering the contactor. In some embodiments, the adjusting the recyclevalve comprises opening or closing the recycle valve based on H₂Scontent in the hydrogen sulfide rich stream. In some embodiments, theadjusting the recycle valve comprises opening the recycle valve when theH₂S content in the hydrogen sulfide rich stream is less than 35% wt. Insome embodiments, the adjusting the recycle valve comprises closing therecycle valve when the H₂S content in the hydrogen sulfide rich streamis greater than or equal to 75% wt.

In some embodiments, the adjusting the recycle valve comprises closingthe recycle valve when a threshold mass flow of the recycled enrichedgas from the regenerator is 20% wt or greater than the acid gas streamto contactor. In some embodiments, the adjusting the recycle valvecomprises closing the recycle valve when on H₂S content in the carbondioxide rich stream is at least 500 ppm. In some embodiments, the methodfurther comprising removing at least a portion of the hydrogen sulfiderich stream exiting from the regenerator from an acid gas enrichmentsystem. In some embodiments, the method further comprising periodicallyremoving at least a portion of the hydrogen sulfide rich stream exitingfrom the regenerator from an acid gas enrichment system.

In a second aspect, a system of enriching acid gas for feeding a sulfurrecovery unit comprises: (i) a contactor configured to separate an acidgas stream into a carbon dioxide rich stream and a purified acid gasstream, the acid gas stream comprising hydrogen sulfide, carbon dioxide,and hydrocarbons; (ii) a regenerator in fluid communication with thecontactor such that the regenerator is configured to separate thepurified acid gas stream to create a hydrogen sulfide rich stream and ahydrogen sulfide lean stream, the hydrogen sulfide rich stream having aconcentration of hydrogen sulfide; and (iii) a recycle stream conduitfluidly coupled between the regenerator to the contactor and configuredto supply at least a portion of the hydrogen sulfide rich stream fromthe regenerator to the contactor.

In some embodiments, the system comprises an acid gas recycle valvecoupled to the recycle stream conduit that opens and closes a fluidpathway from the regenerator to the contactor. In some embodiments, thesystem comprises an acid gas recycle valve coupled to the recycle streamconduit that adjusts a flowrate of a fluid pathway from the regeneratorto the contactor. In some embodiments, the system comprises a singlecontactor. In some embodiments, the system is exclusive of a vacuumspool or a compressor for the contactor.

In a third aspect, a system of enriching acid gas for feeding a sulfurrecovery unit includes: (i) a contactor configured to separate an acidgas stream into a carbon dioxide rich stream and a purified acid gasstream, the acid gas stream comprising hydrogen sulfide, carbon dioxide,and hydrocarbons; (ii) a regenerator in fluid communication with thecontactor, the regenerator configured to separate the purified acid gasstream to create a hydrogen sulfide rich stream and a hydrogen sulfidelean stream, the hydrogen sulfide rich stream having a concentration ofhydrogen sulfide; and (iii) a controller configured to operate a recyclevalve, wherein the recycle valve, when in an open state, is configuredto separate at least a portion of the hydrogen sulfide rich streamexiting from the regenerator and to feed the portion of the hydrogensulfide rich stream to the contactor, and wherein the recycle valve,when in an closed state, is configured to purge an entire hydrogensulfide rich stream exiting from the regenerator.

In some embodiments, the controller is configured to open, partiallyopen, or close the recycle valve. In some embodiments, the controller isconfigured to open the recycle valve when H₂S content in the hydrogensulfide rich stream is less than 35% wt. In some embodiments, thecontroller is configured to close the recycle valve when H₂S content inthe hydrogen sulfide rich stream is greater than or equal to 75% wt. Insome embodiments, the controller is configured to close the recyclevalve when H₂S content in the carbon dioxide rich stream is greater thanor equal to 500 ppm. In some embodiments, the controller is configuredto close the recycle valve when a total mass flow of the recycledenriched gas from the regenerator is 20% wt. or greater than the acidgas stream to contactor.

In example implementations of the present disclosure, “sour gas” isnatural gas or any other gas containing significant amounts of hydrogensulfide, for example, greater than 5.7 milligrams (mg) of H₂S per cubicmeter of natural gas, or at least 4 ppm by volume of H₂S under standardtemperature and pressure.

A “sweet gas” is natural gas that does not contain significant amountsof hydrogen sulfide, for example, less than 5.7 mg of H₂S per cubicmeter of natural gas, or less than 4 ppm by volume of H₂S under standardtemperature and pressure. The term “sweetening” is a process thatremoves H₂S and other organosulfur compounds at an oil refinery or anatural gas processing plant.

A “turn-down-ratio” (TDR), as provided in example implementations ofthis disclosure, is the ratio of the maximum capacity to minimumcapacity. TDR relates to the width of the operational range of a system,for example, the ratio of a design feed rate to a lowest available feedrate.

The features associated with the present disclosure include achieving asignificant increase of H₂S concentration in an enriched acid gas, whichfeeds to a sulfur recovery unit (SRU), using systems and methods ofrecycling enriched acid gas as disclosed herein. Certain embodiments ofthe systems and methods of the present disclosure can improve the H₂Sconcentration of the enriched acid gas, for example, by about 70%-80% ascompared to systems and methods that do not recycle enriched acid gas,based on simulation-based enriched gas H₂S concentration values of thestripper (regenerator) gas outlet as compared to off-gas concentrationvalues from the amine contactor. Certain embodiments of the systems andmethods described herein can advantageously reduce the CO₂ concentrationof the enriched acid gas, for example, by about 15% mole CO₂ to about36% mole CO₂, to allow for increased capacity and sulfur production atthe SRU. Simulation results of the system and methods described hereinshow that recycle enriched acid gas can improve the SRU feeds by 36%, ascompared to the 18% associated with systems and methods that do notrecycle enriched acid gas. The improved enrichment process describedherein can also optimize an acid enrichment process by reducingcontactor solvent (amine) losses in the system. In some embodiments,solvent losses can be reduced by about 50%.

The systems and methods provided herein can provide the benefit ofreprocessing enriched acid gas without the use of duplicate equipment orsystems. Eliminating the need to use additional AGE systems andequipment to further process the enriched acid gas can reduceoperational costs and equipment expenses as well as increase processefficiency and improve gas product yields.

Certain embodiments of the systems and methods provided herein canprovide an added benefit of reducing fuel gas co-firing in the SRU asthe level of acid gas increases in the SRU feed. This fuel gas co-firingreduction can improve catalyst performance and/or reduce H₂Sbreakthrough in a given system.

The present disclosure includes one or more of the following units ofmeasure with their corresponding abbreviations, as shown in Table 1:

TABLE 1 Unit of Measure Abbreviation Degrees Celsius ° C. Megawatts MWOne million MM British thermal unit Btu Grams (weight) g Hour h Poundsper square inch (pressure) psi Kilogram (mass) Kg Second S Cubic metersper day m³/day Fahrenheit F.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example acid gas enrichment system thatrecycles enriched acid gas to optimize the hydrogen sulfide content inthe enriched acid gas.

FIG. 2 is a flowchart of an example recycle-flow decision methodassociated with an acid gas enrichment process.

FIGS. 3A and 3B are flowcharts of an example method of sulfur enrichingan acid gas stream in an acid gas enrichment system.

FIG. 4 is a schematic illustration of an example controller for an acidgas enrichment system that recycles enriched acid gas to optimize thehydrogen sulfide content in the enriched acid gas.

DETAILED DESCRIPTION

This specification describes technologies and methods relating to anacid gas enrichment process that increase a concentration level ofhydrogen sulfide (H₂S) in an enriched acid gas.

FIG. 1 shows a schematic diagram of an example system 100 to sweeten anacid gas that enters as an acid gas input stream 104 (may also bereferred to as sour natural gas) and enrich the acid gas input stream104 to feed a sulfur recovery unit. The example system 100 includes anacid gas enrichment (AGE) contactor 120 (also referred to as anabsorber), which receives an acid gas stream 106 containing the acid gasinput stream 104 (along with a recycled acid gas stream 162, which willbe discussed later). An acid gas stream 106 is a gas stream containinghydrogen sulfide (H₂S). In some embodiments, the acid gas stream 106contains less than about 55 mole percent of H₂S. In some embodiments,acid gas stream 106 contains between about 15 and about 55 mole percentof H₂S, between about 15 and about 50 mole percent of H₂S, between about15 and about 45 mole percent of H₂S, between about 25 and about 55 molepercent of H₂S, between about 35 and about 50 mole percent of H₂S, orbetween about 40 and about 45 mole percent of H₂S. In some embodiments,the acid gas stream 106 can contain greater than 15 mole percent of H₂S.The acid gas stream 106 can include H₂S, CO₂, hydrocarbons, and othercontaminants. In some embodiments, the hydrocarbons present in the acidgas stream 106 can include benzene, toluene, ethyl benzene, and xylene.In some embodiments, the hydrocarbons present in the acid gas stream 106can further include alkanes, alkenes, olefins. In some embodiments, thecontaminants present in acid gas stream 106 can include mercaptans,thiols, carbonyl sulfide, carbon disulfide, and combinations thereof.

The contactor 120 separates the acid gas stream 106 into a carbondioxide rich stream (which may also be referred to as a hydrocarbon richstream) 122 and a purified acid gas stream 124. The carbon dioxide richstream is rich in CO₂ and hydrocarbons, and lean in H₂S. The carbondioxide rich stream is commonly referred to as a sweet gas. The carbondioxide rich stream can contain about 70 to about 99 mole percent ofCO₂, about 85 to about 99% mole percent of CO₂, or greater than 89 molepercent of CO₂. The carbon dioxide rich stream can be further processedby other systems (not shown) for carbon source recovery, hydrocarbonrecovery, or both.

As shown in FIG. 1, the example system 100 includes an acid gasenrichment (AGE) regenerator 140 (may also be referred to as an aminestripper) which is in fluid communication with the contactor 120. Theregenerator 140 receives the purified acid gas stream 124 from thecontactor 120 and separates the purified acid gas stream 124 into ahydrogen sulfide rich stream 142 and a hydrogen sulfide lean stream 144.The hydrogen sulfide rich stream 144 has a significantly higherconcentration of hydrogen sulfide than the hydrogen sulfide lean stream142, for example, a ratio of the molar amount of hydrogen sulfide in thehydrogen sulfide rich stream 144 and the hydrogen sulfide hydrogensulfide lean stream 142 can be about 40.

The example system 100 further includes a recycle stream conduit 160that supplies a portion of the hydrogen sulfide rich stream 162outputted from the regenerator 140 back to the contactor 120. Therecycle stream conduit 160 is fluidly coupled (either directly orindirectly) to the regenerator 140 and the contactor 120. As shown, therecycle steam conduit 160 is coupled to regenerator 140 via a refluxdrum 180 (also referred to as a separator). A portion of the hydrogensulfide rich stream 142 exiting from the reflux drum 180 is recycledback from the regenerator 140 to the contactor 120. In this examplesystem 100, three pumps 170,171,172, one heat exchanger 174, a surgetank 176, a cooler 178, a condenser 179, a reflux drum 180, a reboiler182, and various valves 184 and connectors 186, 187 are used to sweetenand enrich the acid gas in the system 100.

In general, this specification discloses a method of sulfur enriching anacid gas stream using the acid gas enrichment system 100 describedherein. The method includes feeding the acid gas stream 104, 106, whichcontains hydrogen sulfide, carbon dioxide, and hydrocarbons, to thecontactor 120. The method includes separating the acid gas stream 104 inthe contactor 120 to create the carbon dioxide rich stream 122 and thepurified acid gas stream 124, and feeding the purified acid gas stream124 to the regenerator 140, which is fluidly connected to the contactor120. The method also includes separating the purified acid gas stream124 in the regenerator 140 to create the hydrogen sulfide rich stream142 and the hydrogen sulfide lean stream 144. The hydrogen sulfide richstream 142 has a concentration of hydrogen sulfide that is greater thanthe hydrogen sulfide lean stream 144. The method includes periodicallyrecycling at least a portion of the hydrogen sulfide rich stream 162exiting the regenerator 140 back to the contactor 120. In someembodiments, the periodic feeding step includes using a controller 164to open and close a valve 166 disposed along a fluid pathway (forexample, the recycle stream conduit) that directs the hydrogen sulfiderich stream 162 exiting the regenerator 140 to the acid gas stream 106entering the contactor 120.

In the example system 100, the contactor 120 is the first vessel in thesystem 100. The contactor 120 is an 8-tray column that receives souracid gas 106 at the lower portion of the column. The contractor 120introduces a lean solution containing a solvent (which can also bereferred to as a sweetening solvent) in water at the top of the column.The solvent typically includes an amine acid, for example, solventcontaining 30% wt. of methyl di-ethanolamine (MDEA). The solventinteracts with the sour gas 106 as the gas flows upward through columnof the contractor 120 and separates H₂S (and optionally the CO₂,depending on the solvent used) from the acid gas 106. The gas 122 thatreaches the top of the contactor has become a sweet gas. In someembodiments, the contactor 120 can include a column containing 8 to 24trays (for example, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, or 24 trays). In some embodiments, the contactor 120 can bea packed column. In some embodiments, the system 100 includes only asingle contactor 120 because the recycle stream conduit 160 (which willbe discussed in later sections) provides the advantage of returning atleast a portion of the acid gas product exiting from the regenerator 140back to the contactor 120.

As shown, the purified acid gas stream 124 exits from a bottom part ofthe contactor 120. The purified acid gas stream 124 is pumped through aheat exchanger 174, which is heated by the regenerated lean solutionstream 144. The heated purified acid gas stream 126 then flows into atop part of the regenerator 140, the second vessel in the system 100.

In the example system 100, the regenerator 140 is an 11-tray column thatreceives the heated acid gas stream 126 to regenerate the solvent. Insome embodiments, the regenerator 140 can include a column containing 8to 24 trays (for example, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,20, 21, 22, 23, or 24 trays). The regeneration process can occur at apressure of about 12 to 15 psig and at the solution boiling temperature.As shown, the regenerator 140 is heated by an external source, such asan acid gas enrichment reboiler 182. The regenerator 140 separates therich acid gas stream 126 into a hydrogen sulfide rich gas stream 142containing liberated acid gas, hydrocarbon gas, some solvent, and watervapor. The hydrogen sulfide rich gas stream 142 is flowed through acondenser 179 to condense the solvent and water vapors. The reflux drum180 receives the flow of liquid and gas mixture 146 to separate the acidgas 148 from the condensed liquids 150. The liquids 150 are pumped backinto the regenerator 140 as reflux. The gas stream 148 exiting thereflux drum primarily includes H₂S and CO₂. In this example system 100,the enriched acid gas stream 148 exiting from the reflux drum 180 splitsat a split connector 187 to an exit stream 168 and a recycle stream 162.The exit stream 168 delivers enriched acid gas to a SRU.

As shown, the system 100 includes the recycle stream conduit 160 todeliver a recycle stream 162 containing at least a portion of theenriched acid gas 162 exiting from the reflux drum 180 back to thecontactor 120 for carbon dioxide slippage, which is a process thatremoves carbon dioxide from a gas stream. The recycle stream conduit 160serves as a by-pass line of the enriched acid gas 148 exiting from thereflux drum 180. The recycle stream 162 is connected with a virgin acidgas supply stream 104 entering the system at an acid gas streamconnector 186 before to entering the contactor 120. In some embodiments,the recycle stream 162 and the virgin acid gas supply stream 104 canflow directly into the contactor 120 through separate conduits.

The system 100 optionally includes the acid gas recycle valve 166coupled to the recycle stream conduit 160 to open and close a fluidpathway between the regenerator 140 and the contactor 120. The recyclevalve 166 is located between the split connector 187 and the acid gasstream connector 186. The recycle valve 166 can be a pressure controlvalve, a flow rate control valve, or the like. The recycle valve 166allows for a constant or periodic recycle stream of the hydrogen sulfiderich stream 162 from the regenerator 142 to be recycled back as an acidgas stream feed to the contactor 120.

As shown, the system 100 includes a controller 164 connected to therecycle valve 166 that serves to actuate the recycle valve 166 betweenopen and closed states. The controller 164 can be coupled directed to,integrated with, or positioned proximately to the recycle valve 166and/or the recycle stream conduit 160. In some embodiments, thecontroller 164 can actuate the recycle valve 166 to various partiallyobstructed open states to increase or decrease the flowrate of therecycle stream 162 based on a measured parameter, such as a pressureand/or flowrate of one or more streams in the system 100. In someembodiments, the controller 164 can be an optional component, where thesystem 100 may include the acid gas recycle valve 166 coupled to therecycle stream conduit 160 without a controller 164.

The controller 164 can be programmed to actuate the recycle valve 166based on pressure, flowrate, and/or component compositions of a fluidsteam in the system 100. For example, in some embodiments, thecontroller 164 can be a pressure or flowrate valve controller thatactuates between the open and closed states based on pressure orflowrate, respectively. In some embodiments, the controller 164 can beprogrammed to actuate the recycle valve 166 based on the volumetric rateof an acid gas stream 104,106 entering the contactor 120, and/or acidgas stream 148,162 leaving the regenerator 140 and the reflux drum 180.The acid gas steam 104,106 entering the contactor 120 can include acombined acid gas stream 106 (e.g., includes both the recycle stream andthe raw input stream), or an individual acid gas stream (not shown).

In some embodiments, the controller 164 can open or close the recyclevalve 166 based on H₂S content in the recycle stream 162 (e.g., ahydrogen sulfide rich stream). For example, certain configurations ofthe controller 164 can open the recycle valve 166 when a measuredpressure at the recycle valve 166 exceeds a specific pressure value,such as the pressure of the contactor. In some embodiments, thecontroller 164 can open the recycle valve 166 when the H₂S content inthe recycle stream 162 is 35% wt. or less. In some embodiments, thecontroller 164 can open the recycle valve 166 when the H₂S content inrecycle stream 162 is greater than or equal to 75% wt. In someembodiments, wherein the controller 164 can open the recycle valve 166when the H₂S content in the carbon dioxide rich stream 122 is about 500ppm or greater. In some embodiments, the controller can open the recyclevalve based on a total mass flow of an input stream (for example, therecycled enriched gas from amine regenerator can reach 20% wt or greaterthan the acid gas feed stream to amine contactor).

In some embodiments, the controller 164 can be programmed to actuate therecycle valve 166 based on an algorithm that includes one or moreparameters, including pressure, flowrate, mass flow, and componentcompositions of a fluid steam in the system 100. For example, Thecontroller 164 can be programmed with a logic control pressure valvethat operate the recycle valve 166 using a mathematical formula in whicha controller set point is based on the contactor pressure, contactorsolvent (e.g., amine acid) gas volumetric flowrate, and the contactorsolvent (e.g., amine acid) composition. The formula can include avolumetric flowrate adjustment factor that is based on the compositionof the amine used in the system 100. An exemplary algorithm can includea pressure valve set point for actuating (closing) the recycle valve 166based on the contactor pressure and/or the amine acid gas volumetricflowrate, as shown in the following equations:Set point>contactor pressure+3 psig, or  (Eq. 1)Set point>amine acid gas volumetric flowrate×0.1978  (Eq. 2)

FIG. 2 provides a flowchart of an exemplary recycle-flow decision method200 associated with an acid gas enrichment process that uses a recyclevalve controller, as described in this document. The recycle valvecontroller can be a flowrate and/or a pressure controller. As shown inFIG. 2, the method 200 includes operating a gas treatment process, suchas an acid gas enrichment process (Step 210). The enriched acid gas flowrates for acid gas, H₂S, and carbon dioxide, CO₂, in the process areseparately determined (Step 220). When the acid gas H₂S is greater thana desired set point, the recycle valve controller closes the recyclevalve (Step 230). As depicted in Step 230, an acid gas H₂S weightpercentage that is greater than 60 wt. % is the desired set point forthe method 200 in certain embodiments. When the acid gas H₂S is outsidethe range of the desired set point (for example, when the acid gas H₂Sweight percentage is equal to or less than 60 wt. %), the recycle valvecontroller opens the recycle valve (Step 240). In some embodiments, theprocess can optionally include determining a residual factor (Step 250,or Step 270), which is a comparative measurement that compares theenriched acid gas flow rates for H₂S and CO₂ as calculated in apredicted model to measured data collected from the gas treatmentoperation. The residual factor verifies that the recycle valvecontroller is accurately opening and closing the recycle valve based onthe desired set point. Assuming the residual factor is within anacceptable level and the acid gas H₂S is outside the desired set point(acid gas <60 wt. %), the recycle valve will be in an open state (Step240). Alternatively, when the acid gas H₂S is within the desired setpoint (acid gas >60 wt. %), the recycle valve will be in a closed state(Step 260). Furthermore, the recycle valve controller will periodicallyremeasure the enriched acid gas flow rates for H₂S and CO₂ in the gastreatment process (Step 230), and will close or open recycle valve(Steps 240, 260) accordingly.

FIGS. 3A and 3B are flowcharts of an exemplary method 300 of sulfurenriching an acid gas stream using an acid gas enrichment system, asdescribed in this document. As depicted in FIG. 3A, the method 300includes feeding an acid gas stream to a contactor (Step 310). The acidgas stream can include hydrogen sulfide, H₂S, carbon dioxide, CO₂, andhydrocarbons. The method 300 also includes separating the acid gasstream in the contactor to create a carbon dioxide rich stream and apurified acid gas stream (Step 320). The method includes feeding thepurified acid gas stream to a regenerator fluidly connected to thecontactor (Step 330), and separating the purified acid gas stream in theregenerator to create a hydrogen sulfide rich stream and a hydrogensulfide lean stream (Step 340). The method 300 also includesperiodically feeding at least a portion of the hydrogen sulfide richstream exiting the regenerator to the acid gas stream entering thecontactor (Step 350).

As shown in FIG. 3B, the periodic feeding step 350 includes determiningwhether to adjust a recycle valve disposed along a fluid pathway thatdirects the hydrogen sulfide rich stream exiting the regenerator to theacid gas stream entering the contactor (step 351). In some embodiments,adjusting the recycle valve includes adjusting the recycle valve basedon the H₂S content in the hydrogen sulfide rich stream (step 352). Asshown, adjusting the recycle valve can also include closing the recyclevalve based on the H₂S content in the hydrogen sulfide rich stream beinggreater than or equal to 75% wt, in some embodiments. Alternatively,adjusting the recycle valve can include opening the recycle valve basedon the H₂S content in the hydrogen sulfide rich stream being less thanabout 35% wt. (e.g., less than about 30% wt., less than about 25% wt.,less than about 20% wt., less than about 15% wt., less than about 10%wt., or less than about 5% wt.).

Still referring to FIG. 3B, adjusting the recycle valve includes closingthe recycle valve when the total mass flow of the recycled enriched gasfrom amine regenerator is greater than or equal to 20% wt. of the acidgas feed to the amine contactor (Step 353), or when the H₂S content inthe carbon dioxide rich stream is greater than or equal to 500 ppm (Step354). In some embodiments, adjusting the recycle valve includes closingthe recycle valve when the H₂S content in the carbon dioxide rich streamis greater than or equal to 650 ppm, or 900 ppm. Criterion for adjustingthe recycle valve are not limited to only the examples described aboveand can include criterion based on a component weight percent content,flow rate, or pressure value.

Referring back to FIG. 3A, the example method also includes removing atleast a portion of the hydrogen sulfide rich stream exiting from theregenerator from the system. In some embodiments, the removing of thehydrogen sulfide rich stream from the system occurs periodically basedon a desired time frame (for example, once a day, month, or year), orbased on a given component weight percent content, flow rate, orpressure value.

EXAMPLE 1

Table 2 provides a first example of operating conditions and gascompositions of various streams of a system, as obtained by simulationmodels developed in accordance with the system shown in FIG. 1.

TABLE 2 Stream 104 106 122 162 168 Std. Vapor Vol. 1.40 1.72 1.19 0.290.29 Flow (MMSCFD) T (Deg. F.) 91.3 91.6 133.05 95.9 95.9 P (psia) 17.512.6 11.5 12.6 12.6 Component Hydrogen sulfide 9.2 15.9 269.28 ppm 44.544.5 (mol. %, unless indicated otherwise) Carbon dioxide 87.1 80.5 89.752.3 52.3 (mol. %) Hydrogen sulfide 5248.4 11198.0 13.1 5181.6 5181.6(Mass flow, kg/d)

In this first example, the controller was programmed to open and closeof the recycle valve to achieve a hydrogen sulfide concentration leveland mass flow in the enriched acid gas stream (Stream 168) of 44.5% mol.and 5,181 kilograms per day (kg/d), respectively.

EXAMPLE 2

Table 3 provides a second example of operating conditions and gascompositions of various streams of a system, as obtained by simulationmodels developed in accordance with the system shown in FIG. 1. In thissecond example, the controller was programmed to open and close of therecycle valve to achieve a hydrogen sulfide concentration level and massflow in the enriched acid gas stream (Stream 168) of 47.8% mol. and6,819 kilograms per day (kg/d), respectively.

TABLE 3 Stream 104 106 122 162 168 Std. Vapor Vol. 1.44 1.79 1.17 0.350.35 Flow (MMSCFD) T (Deg. F.) 91.3 91.6 133.04 95.9 95.9 P (psig) 17.512.6 11.5 12.6 12.6 Component Hydrogen sulfide 11.8 18.8 388.41 ppm 47.847.8 (mol. %, unless indicated otherwise) Carbon dioxide 84.7 77.7 89.749.0 49.0 (mol. %) Hydrogen sulfide 6831.9 13651.0 18.4 6819.1 6819.1(Mass flow, kg/d)

EXAMPLE 3

Table 4 below provides a third example of operating conditions and gascompositions of various streams of a system, as obtained by simulationmodels developed in accordance with the system shown in FIG. 1. In thisthird example, the controller was programmed to open and close of therecycle valve to achieve a hydrogen sulfide concentration level and massflow in the enriched acid gas stream (Stream 168) of 51.6% mol. and9,454 kilograms per day (kg/d), respectively.

TABLE 4 Stream 104 106 122 162 168 Std. Vapor Vol. 1.50 1.74 1.13 0.440.45 Flow (MMSCFD) T (Deg. F.) 91.3 91.3 133.02 95.9 95.9 P (psig) 17.512.6 11.5 12.6 12.6 Component Hydrogen sulfide 15.5 20.4 461.8 ppm 51.651.6 (mol. %, unless indicated otherwise) Carbon dioxide 84.7 76.1 89.645.3 45.3 (mol. %) Hydrogen sulfide 9460.8 14440.0 21.2 9454.4 9454.4(Mass flow, kg/d)

FIG. 4 is a schematic illustration of an example controller 300 (orcontrol system) for an acid gas enrichment system that recycles enrichedacid gas to optimize the hydrogen sulfide content in the enriched acidgas. In some aspects, the controller 300 may include the controller 330shown in FIG. 4.

The controller 300 is intended to include various forms of digitalcomputers, such as printed circuit boards (PCB), processors, digitalcircuitry, or otherwise that is part of a vehicle. Additionally thesystem can include portable storage media, such as, Universal Serial Bus(USB) flash drives. For example, the USB flash drives may storeoperating systems and other applications. The USB flash drives caninclude input/output components, such as a wireless transmitter or USBconnector that may be inserted into a USB port of another computingdevice.

The controller 300 includes a processor 310, a memory 320, a storagedevice 330, and an input/output device 340. Each of the components 310,320, 330, and 340 are interconnected using a system bus 350. Theprocessor 310 is capable of processing instructions for execution withinthe controller 300. The processor may be designed using any of a numberof architectures. For example, the processor 310 may be a CISC (ComplexInstruction Set Computers) processor, a RISC (Reduced Instruction SetComputer) processor, or a MISC (Minimal Instruction Set Computer)processor.

In one implementation, the processor 310 is a single-threaded processor.In another implementation, the processor 310 is a multi-threadedprocessor. The processor 310 is capable of processing instructionsstored in the memory 320 or on the storage device 330 to displaygraphical information for a user interface on the input/output device340.

The memory 320 stores information within the controller 300. In oneimplementation, the memory 320 is a computer-readable medium. In oneimplementation, the memory 320 is a volatile memory unit. In anotherimplementation, the memory 320 is a non-volatile memory unit.

The storage device 330 is capable of providing mass storage for thecontroller 300. In one implementation, the storage device 330 is acomputer-readable medium. In various different implementations, thestorage device 330 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 340 provides input/output operations for thecontroller 300. In one implementation, the input/output device 340includes a keyboard and/or pointing device. In another implementation,the input/output device 340 includes a display unit for displayinggraphical user interfaces.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, forexample, in a machine-readable storage device for execution by aprogrammable processor; and method steps can be performed by aprogrammable processor executing a program of instructions to performfunctions of the described implementations by operating on input dataand generating output. The described features can be implementedadvantageously in one or more computer programs that are executable on aprogrammable system including at least one programmable processorcoupled to receive data and instructions from, and to transmit data andinstructions to, a data storage system, at least one input device, andat least one output device. A computer program is a set of instructionsthat can be used, directly or indirectly, in a computer to perform acertain activity or bring about a certain result. A computer program canbe written in any form of programming language, including compiled orinterpreted languages, and it can be deployed in any form, including asa stand-alone program or as a module, component, subroutine, or otherunit suitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having a display device such as a CRT (cathode ray tube)or LCD (liquid crystal display) monitor for displaying information tothe user and a keyboard and a pointing device such as a mouse or atrackball by which the user can provide input to the computer.Additionally, such activities can be implemented via touchscreenflat-panel displays and other appropriate mechanisms.

The features can be implemented in a control system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include a local area network (“LAN”),a wide area network (“WAN”), peer-to-peer networks (having ad-hoc orstatic members), grid computing infrastructures, and the Internet.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features that are described in this specification inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. For example, exampleoperations, methods, or processes described herein may include moresteps or fewer steps than those described. Further, the steps in suchexample operations, methods, or processes may be performed in differentsuccessions than that described or illustrated in the figures.Accordingly, other implementations are within the scope of the followingclaims.

The invention claimed is:
 1. A system of acid gas enrichment, the systemcomprising: an acid gas stream connector configured to receive an acidgas stream; a contactor configured to separate the acid gas streamreceived from the acid gas stream connector into a carbon dioxide richstream and a purified acid gas stream, the acid gas stream comprisinghydrogen sulfide (H₂S), carbon dioxide (CO₂), and hydrocarbons; aregenerator in fluid communication with the contactor such that theregenerator is configured to separate the purified acid gas stream toobtain a hydrogen sulfide rich stream and a hydrogen sulfide leanstream, the hydrogen sulfide rich stream having a concentration ofhydrogen sulfide; a recycle stream conduit fluidly coupled between theregenerator and the contactor, and configured to supply at least aportion of the hydrogen sulfide rich stream from the regenerator to thecontactor; and an acid gas recycle valve coupled to the recycle streamconduit that opens and closes a fluid pathway from the regenerator tothe contactor based on an H₂S content in the hydrogen sulfide richstream to direct the hydrogen sulfide rich stream exiting theregenerator to combine with the acid gas stream at the acid gas streamconnector prior to the combination of the hydrogen sulfide rich streamand the acid gas stream entering the contactor.
 2. The system of claim1, wherein the system comprises a single contactor.
 3. The system ofclaim 1, wherein the system is exclusive of a vacuum spool or acompressor for the contactor.
 4. A system of acid gas enrichment, thesystem comprising: an acid gas stream connector configured to receive anacid gas stream; a contactor connected to the acid gas stream connectorby a conduit, the contactor configured to separate the acid gas streamfrom the acid gas stream connector into a carbon dioxide rich stream anda purified acid gas stream, the acid gas stream comprising hydrogensulfide (H₂S), carbon dioxide (CO₂), and hydrocarbons; a regenerator influid communication with the contactor, the regenerator configured toseparate the purified acid gas stream to obtain a hydrogen sulfide richstream and a hydrogen sulfide lean stream, the hydrogen sulfide richstream having a concentration of hydrogen sulfide; a recycle valvepositioned in another conduit between the regenerator and the acid gasstream connector to direct the hydrogen sulfide rich stream exiting theregenerator to combine with the acid gas stream at the acid gas streamconnector prior to the combination of the hydrogen sulfide rich streamand the acid gas stream entering the contactor; and a controllerconfigured to operate the recycle valve based on an H₂S content in thehydrogen sulfide rich stream, wherein the recycle valve, when in an openstate, is configured to separate at least a portion of the hydrogensulfide rich stream exiting from the regenerator and to feed the portionof the hydrogen sulfide rich stream to the contactor, and wherein therecycle valve, when in an closed state, is configured to purge an entirehydrogen sulfide rich stream exiting from the regenerator.
 5. The systemof claim 4, wherein the controller is configured to open, partiallyopen, or close the recycle valve.
 6. The system of claim 4, wherein thecontroller is configured to open the recycle valve when the H₂S contentin the hydrogen sulfide rich stream is less than 35% wt.
 7. The systemof claim 4, wherein the controller is configured to close the recyclevalve when the H₂S content in the hydrogen sulfide rich stream isgreater than or equal to 75% wt.
 8. The system of claim 4, wherein thecontroller is configured to close the recycle valve when an H₂S contentin the carbon dioxide rich stream is greater than or equal to 500 ppm.9. The system of claim 4, wherein the controller is configured to closethe recycle valve when a total mass flow of the recycled hydrogensulfide rich stream from the regenerator is 20% wt. or greater than theacid gas stream to the contactor.
 10. The system of claim 1, wherein theacid gas recycle valve is configured to open when the H₂S content in thehydrogen sulfide rich stream is less than 35% wt.
 11. The system ofclaim 1, wherein the acid gas recycle valve is configured to open whenthe H₂S content in the hydrogen sulfide rich stream is greater than orequal to 75% wt.
 12. The system of claim 1, wherein the acid gas recyclevalve is configured to open when an H₂S content in the carbon dioxiderich stream is greater than or equal to 500 ppm.
 13. The system of claim1, wherein the acid gas recycle valve is configured to close when atleast one of: the H₂S content in the hydrogen sulfide rich stream isgreater than or equal to 75% wt; a threshold mass flow of the recycledhydrogen sulfide rich stream from the regenerator is 20% wt or greaterthan a mass flow of the acid gas stream to the contactor; or an H₂Scontent in the carbon dioxide rich stream is at least 500 ppm.
 14. Thesystem of claim 1, wherein the acid gas recycle valve is configured toclose when: the H₂S content in the hydrogen sulfide rich stream isgreater than or equal to 75% wt; a threshold mass flow of the recycledhydrogen sulfide rich stream from the regenerator is 20% wt or greaterthan a mass flow of the acid gas stream to the contactor; and an H₂Scontent in the carbon dioxide rich stream is at least 500 ppm.
 15. Thesystem of claim 1, wherein the acid gas recycle valve is configured toopen or close based on an operating pressure of the contactor.
 16. Thesystem of claim 4, wherein the controller is configured to determine aresidual factor based on a flow rate of the hydrogen sulfide rich streamand a flow rate of the carbon dioxide rich stream.
 17. The system ofclaim 16, wherein the residual factor comprises a comparativemeasurement that compares flow rates of the hydrogen sulfide rich streamand the carbon dioxide rich stream in a predicted model to measured flowrates of the hydrogen sulfide rich stream and the carbon dioxide richstream.
 18. The system of claim 16, wherein the controller is configuredto: (i) determine that the residual factor is within an acceptablelevel; (ii) determine a measured flow rate of the hydrogen sulfide richstream is outside of an acceptable level; and (iii) based on thedeterminations in (i) and (ii), adjust the recycle value toward an openstate or maintaining the recycle valve at the open state.
 19. The systemof claim 16, wherein the controller is configured to: (i) determine thatthe residual factor is within an acceptable level; (ii) determine ameasured flow rate of the hydrogen sulfide rich stream is within anacceptable level; and (iii) based on the determinations in (i) and (ii),adjust the recycle value toward a closed state or maintaining therecycle valve at the closed state.
 20. The system of claim 16, whereinthe controller is configured to open or close the recycle valve based onan operating pressure of the contactor.